Zoology 106 Lab Mollusca
Zoology 106 Lab Mollusca Bio 106-016
Kutztown University of Pennsylvania
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This 6 page Class Notes was uploaded by Dallas Bowe on Thursday March 3, 2016. The Class Notes belongs to Bio 106-016 at Kutztown University of Pennsylvania taught by Dr. Nancy Butler in Spring 2016. Since its upload, it has received 42 views. For similar materials see Zoology Lab in Biology at Kutztown University of Pennsylvania.
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Date Created: 03/03/16
Chapter 10: Molluscs Kingdom: Animalia Phylum: Mollusca Bilateral symmetry Unsegmented True coelom Dioecious Cephalization varies Protostomes Adaptive radiation evolution of numerous species from a common ancestor following migration into a new environment o accelerated when the new environment has few existing competitors; the introduced organisms disperse quickly to different niches 4 major morphological features: 1. protective shell 2. visceral mass to house major internal organs 3. mantle 4. foot for locomotion Class and Characteristics Representative Animals Gastropoda Welldeveloped head with eyes and tentacles; body undergoes (~60,000 sp.) torsion during development; primarily marine; w/ some freshwater Snails, slugs and terrestrial species nudibranchs Bivalvia 2 part, hinged shell; reduced head; marine or freshwater filter (~20,000 sp.) feeders Clams, oysters, mussels, scallops Polyplacophora Dorsal shell consists of 8 overlapping plates; unsegmented ventral (~900 sp.) body with headfoot; entirely marine; herbivore Chitons Scaphopoda Body enclosed in onepiece, curved, conical shell open at both ends; (~900 sp.) mouth with tentacles; head absent, entirely marine Tusk shells Cephalopoda Foot modified into tentacles; shell greatly reduced; prominent head (~786 sp.) with welldeveloped eyes and back; closed circulatory system; Squids, octopuses, entirely marine, highlyactive predators nautiluses Class Bivalvia (Clams and Mussels) Genus:Anadonta and Unio (freshwater mussels) Stationary filterfeeders; rely on incurrent water flow to bring small food particles and oxygen to their gills and excurrent water flow to carry off carbon dioxide, metabolic wastes and indigestible matter Burrow beneath the sand and extend their siphons through the sand to filter water into their bodies and extract oxygens and nutrients Possess posterior adductor muscles (large) and anterior adductor muscles (small) that allow the clam to close with huge force Incurrent and excurrent siphons small openings in the mantle between the closed bivalves that allow water to pass in and out of the shell Open circulatory system w/ heart blood is not confined within vessels o enters through...Ostia opening in the heart; allow the heart to collect the oxygenated blood from the gills that returns via open sinuses around the heart o pumped out of heart through arteries to mantle, foot, visceral mass where its empties into open sinuses into tissues o small veins collect the blood and return it to gills Pericardial membrane mesodermal tissue that encloses the mussel’s coelom Dioecious (sexes are separate) Sexual reproduction; sperm released from male, female brood fertilized eggs in special pouches of gills until eggs are ready to hatch, eggs develop into larvae called glochidia Glochidia attach to the gills of certain species of fish and act as ectoparasites, later detach when mature and settle at bottom of sea Depend on a constant flow of water through body for acquiring oxygen and nutrients and releasing gametes and wastes 1. Water enters through ventral incurrent siphon to gills 2. Gills extract oxygen, food particles are trapped in mucus and debris is filtered out 3. Water passes through dorsal areas, nitrogenous waste are secreted by kidney 4. Water exits through excurrent siphon through anus Structure Function Incurrent and extendable, fleshy tubes that transport water into and out of the body excurrent siphons Gills Used primarily for respiration and filterfeeding; female freshwater mussels brood eggs in special gill pouches Mantle thin membrane that secretes the shell Shell hard outer covering that protects soft internal organs; composed of a mixture of calcium carbonate and protein Foot muscular region adjacent to visceral mass; used for burrowing and locomotion Visceral mass pouch that houses several major internal organs Adductor muscles large, tubular muscles located at the anterior and posterior ends of the animal; close shell and hold valves tightly together Labial palps fleshy folds of skin located near the mouth that collect food particles from gills and transport them to the mouth Mouth ingestion of food Esophagus short tube through which food passes from the mouth to stomach (rarely visible on dissection) Stomach small chamber located within visceral mass for food storage Digestive gland greenish, granular tissue that secretes digestive enzymes into stomach and intestine to assist in the chemical breakdown Intestine Coiled digestive tract where absorption of nutrients occurs Anus elimination of indigestible wastes (egestion) Gonads produces gametes for reproduction Heart muscular portion of circulatory system that receives blood from the gills and pumps it through short arteries to neighboring tissues and organs Kidney (nephridium) excretory organ of bivalve that filters nitrogenous waste from the hemolymph and eliminates them from the body Class Cephalopoda (Squid and Octopus) (“headfoot”) Genus: Loligo Highly active Visually oriented predators Modified headfoot at one end Tentacles, visceral mass, and arms at other end Nautilus only cephalopod that possess an external shell; no shell in others Squids and cuttlefish use muscular fins for locomotion o Jet propulsion rapidly expelling water from their mantle cavity through their siphon o Jet propulsion are for speedy getawaysno shell; slow them down negative consequence: lack of protection and increased vulnerability from predators new defense mechanisms: mimicry w/ chromatophores and ink sacs o Ink sacs discharge, dark, cloudy liquid through the anus to confuse predators momentarily and provide them a few extra seconds for escape o Chromatophores specialized epidermal cells that allow species to blend in with environment Squid 8 arms (covered in suckers), 2 long tentacles (suckers at distal ends) Radula a conveyor belt of tiny teeth inside the mouth that most mollusc species possess External Anatomy of a Cephalopod (Squid) Structure Function Collar fleshy border separating headfoot region from visceral mass (mantle) Eyes imageforming organs for detecting visual stimuli Siphon hollow tube through which water is expelled from the mantle cavity at high velocity to propel the squid through the water Mantle Body tube encircling visceral mass forming a hollow chamber in which water is collected and used for propulsion Arms Shorter appendages (8) used to manipulate captured prey and act as a rudder for navigating while swimming Tentacle Long, extensible, prehensile appendages (2) for capturing prey s Fins Triangularshaped extensions of the dorsal end of the body tube that are used for leisurely swimming and for maneuvering during locomotion Reproductive system Hectocotylus carries spermatophores to the female’s mantle; modified male arm Males die after mating Internal Anatomy of a Cephalopod (Squid) Structure Function Gills paired, feathery organs used for respiration Esophagus thin tube connected the mouth to the stomach Stomach small sac where food is stored and digested; digestion is entirely extracellular in cephalopods Pancreas small, granular digestive gland that secretes enzymes into the stomach to assist in the breakdown of food Liver large, elongated gland that releases secretions into the stomach to facilitate enzymatic digestion of food Cecum large, thinwalled digestive chamber prominent along the dorsal end of the body Rectum portion of digestive tract leading to anus Ink sac large sac that opens the rectum and secretes a dark brown or black fluid when the animal is alarmed Anus terminal portion of digestive tract located near siphon Testis (male) produces sperm; located in dorsal end of body tube Vas deferens (male) openended chamber that receives and stores sperm Spermatophoric coiled, convoluted tubules that package sperm cells into gland (male) spermatophore packets Penis (male) muscular organ that gathers spermatophores and releases them outside the body where they are transferred by the males’ hectocotylus to the female during mating Ovary (female) site of egg production Oviduct (female) openended chamber that receives eggs from the ovary Nidamental gland produces secretions that form an encasement around the strings of (female) eggs to protect them; nasty taste repels predators Retractor muscles long muscles that control the retraction of the siphon and the head Kidney excretory organ located b/n the gills that filter nitrogenous wastes from the hemolymph and eliminates them from the body Systemic heart large, muscular ventricle that receives oxygenated blood from the gills and pumps it throughout the body Branchial hearts smaller, muscular chambers that receive deoxygenated blood from all parts of the body and pump blood to the gills Closed circulatory system 3 hearts o 1 large systemic heart o 2 small branchial hearts (near base of gills) Systemic heart o receives blood from gills from left and right brachial veins o sent out of heart through anterior aorta, posterior aorta, and genital artery posterior aorta splits into a median mantle artery and 2 lateral mantle arteries anterior vena cava returns deoxygenated blood from head and arms w/ 2 branches to branchial heart o Left and right posterior vena cava collect deoxygenated blood from dorsal portion of the mantle and route it to the branchial hearts o each branchial heart pumps blood to gill for oxygenation through a branchial artery Cephalopod Eye resembles eyes of vertebrates (i.e. convergence evolution) Contain lens, cornea, iris, ciliary muscles, and a retina lens is rigid; retina focuses image by alternating distance b/n lens and retina photoreceptor receive light no blind spots o improves survival; bigger visual range to spot predators
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